1. Field of the Invention
The present invention relates to a soft-switching control device that operates a switching element configuring a power conversion circuit and a method of manufacturing the soft-switching control device. In the soft-switching control device, soft-switching is performed to switch the state of the switching element by controlling a delay time of a timing at which the switching state is switched in relation to a reference timing.
2. Description of the Related Art
As a power conversion circuit enabling soft-switching, a power conversion circuit is proposed (JP-A-2008-283815, and “Research on soft-switching circuit system for power converters in the field of next-generation clean energy applications”, available at the www site: kawalab.dnj.ynu.ac.jp/research/power_electronics/Chopper/Chopper1.html in which a capacitor is connected in parallel with a main switching element of a boost chopper circuit, and an auxiliary switching element, an auxiliary inductor, and the like are provided. Specifically, a delay time of a timing at which the main switching element is switched to an ON-state in relation to a timing at which the auxiliary switching element is switched to an ON-state is controlled. As a result, the main switching element is switched to the ON-state at a timing at which the electrical charge of the capacitor connected in parallel with the main switching element becomes zero. Thus, switching to the ON-state is performed by zero-voltage switching (ZVS).
However, when above-described soft-switching is performed, the delay time is required to be controlled with high accuracy. Therefore, soft-switching may not be able to be appropriately performed when deviation attributed to individual differences and the like occurs between the timings at which ON operation commands for the auxiliary switching element and the main switching element are given and the timings at which the auxiliary switching element and the main switching element are actually switched to the ON-state. The inventors and others have found that such instances actually occur as a result of use of a drive system of a power conversion circuit that performs conventional hard-switching.
In the power conversion circuit that performs conventional hard-switching, delay time adjustment is only required to set a dead time for turning OFF both of a pair of switching elements driven complementarily. The dead time is merely required to be set to prevent with certainty a period where both switching elements are in an ON-state. Therefore, a sufficient margin is ordinarily provided. The effects that setting such margins have on control can be compensated with relative ease by correcting operation signals of the switching elements, such as in a known dead time compensation technique. Conversely, because the effect of soft-switching decreases regardless of the length of the delay time, a method in which a margin is set as described above cannot be used.
The above-described circumstances where soft-switching may not be able to be appropriately performed are not limited to the power conversion circuit, and are generally common in instances where soft-switching is performed to switch the switching state of the switching element by controlling the delay time of the timing at which the switching state is switched relative to the reference timing.